ABSTRACTC57BL/6 mice genetically deficient in interleukin 15 (IL-15(-/-) mice) were generated by gene targeting. IL-15(-/-) mice displayed marked reductions in numbers of thymic and peripheral natural killer (NK) T cells, memory phenotype CD8(+) T cells, and distinct subpopulations of intestinal intraepithelial lymphocytes (IELs). The reduction but not absence of these populations in IL-15(-/-) mice likely reflects an important role for IL-15 for expansion and/or survival of these cells. IL-15(-/-) mice lacked NK cells, as assessed by both immunophenotyping and functional criteria, indicating an obligate role for IL-15 in the development and functional maturation of NK cells. Specific defects associated with IL-15 deficiency were reversed by in vivo administration of exogenous IL-15. Despite their immunological defects, IL-15(-/-) mice remained healthy when maintained under specific pathogen-free conditions. However, IL-15(-/-) mice are likely to have compromised host defense responses to various pathogens, as they were unable to mount a protective response to challenge with vaccinia virus. These data reveal critical roles for IL-15 in the development of specific lymphoid lineages. Moreover, the ability to rescue lymphoid defects in IL-15(-/-) mice by IL-15 administration represents a powerful means by which to further elucidate the biological roles of this cytokine.

Figure 4: IL-15−/− mice have a deficiency in selective populations of IELs. IELs were isolated from individual 8-wk-old female C57BL/6 or IL-15−/− mice (n = 3/group). The isolated IELs were pooled after the individual cell yields were determined for each mouse. The pooled samples were incubated with the indicated mAb and analyzed using three-color flow cytometry. Viable lymphocytes were gated on the basis of forward and side scatter. A total of 200,000 events was collected for each sample. (A–D) IELs were incubated with mAb specific for CD3, Thy1.2, and TCR-α/β or TCR-γ/δ. Gated populations of CD3+ IELs were analyzed for expression of Thy1.2 and TCR-α/β (A and B) or Thy1.2 and TCR-γ/δ (C and D). The numbers shown represent the percentage of CD3+ IELs within each quadrant. (E–H) IELs were incubated with mAb specific for TCR-α/β, CD8α, and CD4 or CD8β. Gated populations of TCR-α/β+ IELs were analyzed for expression of CD4 and CD8α (E and F) or CD8β and CD8α (G and H). The numbers shown represent the percentage of TCR-α/β+ IELs within each quadrant.

Mentions:
IELs were isolated from individual C57BL/6 or IL-15−/− mice, and cell yields were determined. Once isolated, the IEL populations from individual mice were pooled and analyzed by three-color flow cytometry for expression of various cell surface markers. The absolute number of CD3+ IELs isolated from IL-15−/− mice was estimated to be approximately twofold lower than that of control mice. Within the CD3+ populations, the ratio of α/β to γ/δ IELs was ∼1:1 in control and 2:1 in IL-15−/− mice (data not shown). Thy1− IELs, which made up ∼50% of IEL populations in control mice (Fig. 4A and Fig. C), accounted for <5% of the total IELs in IL-15−/− mice (Fig. 4B and Fig. D). Within gated populations of TCR-α/β+ IELs, there were increases in the relative proportions of CD4+CD8− and CD4+CD8+ IELs in IL-15−/− mice compared with the controls (Fig. 4E and Fig. F). However, as the yield of CD3+ IELs from IL-15−/− mice was approximately twofold lower than that of control mice, the changes in the relative proportions of these IEL populations likely arise solely from a decrease in the absolute number of TCR-α/β+ CD4−CD8+ IELs in IL-15−/− mice compared with controls. The decrease in the TCR-α/β+CD4−CD8+ IEL population in IL-15−/− mice resulted from a selective decrease in the subset of IELs that express the CD8αα homodimer (Fig. 4G and Fig. H). Thus, IL-15−/− mice have a dramatic reduction in the specific IEL populations that are thought to arise or mature independently of the thymus.

Figure 4: IL-15−/− mice have a deficiency in selective populations of IELs. IELs were isolated from individual 8-wk-old female C57BL/6 or IL-15−/− mice (n = 3/group). The isolated IELs were pooled after the individual cell yields were determined for each mouse. The pooled samples were incubated with the indicated mAb and analyzed using three-color flow cytometry. Viable lymphocytes were gated on the basis of forward and side scatter. A total of 200,000 events was collected for each sample. (A–D) IELs were incubated with mAb specific for CD3, Thy1.2, and TCR-α/β or TCR-γ/δ. Gated populations of CD3+ IELs were analyzed for expression of Thy1.2 and TCR-α/β (A and B) or Thy1.2 and TCR-γ/δ (C and D). The numbers shown represent the percentage of CD3+ IELs within each quadrant. (E–H) IELs were incubated with mAb specific for TCR-α/β, CD8α, and CD4 or CD8β. Gated populations of TCR-α/β+ IELs were analyzed for expression of CD4 and CD8α (E and F) or CD8β and CD8α (G and H). The numbers shown represent the percentage of TCR-α/β+ IELs within each quadrant.

Mentions:
IELs were isolated from individual C57BL/6 or IL-15−/− mice, and cell yields were determined. Once isolated, the IEL populations from individual mice were pooled and analyzed by three-color flow cytometry for expression of various cell surface markers. The absolute number of CD3+ IELs isolated from IL-15−/− mice was estimated to be approximately twofold lower than that of control mice. Within the CD3+ populations, the ratio of α/β to γ/δ IELs was ∼1:1 in control and 2:1 in IL-15−/− mice (data not shown). Thy1− IELs, which made up ∼50% of IEL populations in control mice (Fig. 4A and Fig. C), accounted for <5% of the total IELs in IL-15−/− mice (Fig. 4B and Fig. D). Within gated populations of TCR-α/β+ IELs, there were increases in the relative proportions of CD4+CD8− and CD4+CD8+ IELs in IL-15−/− mice compared with the controls (Fig. 4E and Fig. F). However, as the yield of CD3+ IELs from IL-15−/− mice was approximately twofold lower than that of control mice, the changes in the relative proportions of these IEL populations likely arise solely from a decrease in the absolute number of TCR-α/β+ CD4−CD8+ IELs in IL-15−/− mice compared with controls. The decrease in the TCR-α/β+CD4−CD8+ IEL population in IL-15−/− mice resulted from a selective decrease in the subset of IELs that express the CD8αα homodimer (Fig. 4G and Fig. H). Thus, IL-15−/− mice have a dramatic reduction in the specific IEL populations that are thought to arise or mature independently of the thymus.

ABSTRACTC57BL/6 mice genetically deficient in interleukin 15 (IL-15(-/-) mice) were generated by gene targeting. IL-15(-/-) mice displayed marked reductions in numbers of thymic and peripheral natural killer (NK) T cells, memory phenotype CD8(+) T cells, and distinct subpopulations of intestinal intraepithelial lymphocytes (IELs). The reduction but not absence of these populations in IL-15(-/-) mice likely reflects an important role for IL-15 for expansion and/or survival of these cells. IL-15(-/-) mice lacked NK cells, as assessed by both immunophenotyping and functional criteria, indicating an obligate role for IL-15 in the development and functional maturation of NK cells. Specific defects associated with IL-15 deficiency were reversed by in vivo administration of exogenous IL-15. Despite their immunological defects, IL-15(-/-) mice remained healthy when maintained under specific pathogen-free conditions. However, IL-15(-/-) mice are likely to have compromised host defense responses to various pathogens, as they were unable to mount a protective response to challenge with vaccinia virus. These data reveal critical roles for IL-15 in the development of specific lymphoid lineages. Moreover, the ability to rescue lymphoid defects in IL-15(-/-) mice by IL-15 administration represents a powerful means by which to further elucidate the biological roles of this cytokine.